Time-Shrinking: The Process of Unilateral Temporal Assimilation

Our previous research on auditory time perception showed that the duration of empty time intervals shorter than about 250 ms can be underestimated hugely if they are immediately preceded by shorter time intervals. We named this illusion ‘time-shrinking’ (TS). This study comprises four experiments in which the preceding interval, t 1 , was followed by a standard interval, t 2 . When t 1 ⩽ 200 ms, and t 1 ⩽ t 2 , the underestimation of t 2 came into view clearly. The absolute difference between t 2 and t 1 was the crucial factor for the illusion to appear. The underestimation increased when t 2 increased from t 1 to t 1 + 65 ms, stayed at about 45 ms when t 2 was between t 1 + 65 ms and t 1 + 95 ms, and disappeared suddenly when t 2 exceeded t 1 + 95 ms. This pattern of results was observed across all values of t 1 ⩽ 200 ms. A model was fit to the data to elucidate the underlying process of the illusion. The model states that the perceived duration difference between t 1 and t 2 is reduced by cutting mental processing time for t 2 ; in other words, that t 2 assimilates to t 1 .